Many contemporary wireless terminals, such as cell phones, are less than 11 centimeters in length. Thus, there is an interest in antennas that can be mounted inside these types of wireless terminals. A planar antenna, such as an planar inverted-F antenna, is one type of antenna that may be well suited for use within the confines of small wireless terminals. Typically, conventional inverted-F antennas include a conductive element that is spaced apart from a ground plane. Exemplary inverted-F antennas are described, for example, in U.S. Pat. Nos. 6,639,560 and 6,573,869, the disclosures of which are incorporated herein by reference in their entireties.
Wireless terminals may operate in multiple frequency bands in order to provide operations in multiple communications systems. For example, many cellular telephones are now designed for dual-band or triple-band operation in GSM and CDMA modes at nominal frequencies of 850 MHz, 900 MHz, 1800 MHz and/or 1900 MHz. Digital Communications System (DCS) is a digital mobile telephone system that typically operates in a frequency band between 1710 MHz and 1850 MHz. The frequency bands allocated for mobile terminals in North America also include 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Depending on the location, a wireless terminal may support communications in two or more of these frequency bands, which is referred to herein as multi-band operations.
Many of the conventional antennas discussed above include a Radio Frequency (RF) “feed” and a ground contact so that a transceiver in the wireless terminal can transmit and receive radio signals in each of the supported frequency bands via the antenna. In some conventional multi-band antenna configurations, it is known to separate the RF feed from ground contact by about 2-3 mm for operation in a low frequency band (e.g., 824-894 MHz.) whereas operations in a high frequency band may require that the RF feed and the ground contact be spaced-apart by distances greater than 2-3 mm. In some multi-band antenna configurations, it is known to space the RF feed and the ground contact apart by about 7-11 mm as a compromise between high and low frequency band performance.
Some conventional multi-band antenna configurations include a grounded parasitic element. Such an approach may require at least one additional contact (i.e. in addition to the RF feed and ground contacts discussed above) to ground, which may require additional space in the wireless terminal to accommodate the antenna. This may decrease the available area for placement of other components within the housing of the wireless terminal.